GPL or other open license, what is the difference? Open is open - maybe

Over the years I have grown to respect and admire Matt Asay as an open source expert.  Matt worked at Novell and did a lot to help them embrace open source and for some time has been at Alfresco Software, who markets an open source ECM.  He and Dave Rosenberg also author the Open Sources blog over at InfoWorld.  Matt was quite excited yesterday announcing that Alfresco went 100% GPL.  Readers of my blog know that open source licensing is something I am interested in, so I read the article eagerly and after it confused me did a little more digging.  Before I go any further, let me say that I don't hold myself out to be the open source expert Matt is and hope that he responds and clarifies this for me.  That being said, I don't get it. 

Matt's article points out what a great thing it is for Alfresco to move from a proprietary but none the less open source license to a fully "100% GPL" model.  He says it is great for users, partner, OEMs, and even the competition (if they will join Alfresco).  So I am thinking, what has Alfresco gained by moving to GPL.  First I thought, that it would allow 3rd parties to use the software in their products and themselves profit from it.  How does that help Alfresco?  But looking in the FAQ, that would not qualify for using the GPL license. You would actually need the commercial license. Commercial license?  What about 100% GPL.  That is what I thought too. 

Digging a little further it seems the GPL part is if you are a regular community user or if you yourself distribute or have a derivative of Alfresco that you distribute as open source under the GPL or some other FLOSS acceptable license (FLOSS is a group of open source licenses that some companies like MySQL group with their GPL stuff).  So now I ask myself, what did these people operate under before the GPL.  It seems Alfresco had their own open source type of license.  Again only for community users and partners who also distribute under open source.  So Matt, I am confused, what did your users really gain? It was free before, it is free now. They had access to source before, they do now. The fact that the GPL is an independent license written and maintained by an entity other than Alfresco.  Is that what the shouting is all about?  Enlighten me please.  GPL or not, your source was open, it was free to community members and I assume commercial partners or users are under a pay license as part of a dual license model.  So what is new and what is the big deal about moving to GPL?  I am not sure the end user is going to realize the subtlety of this move, I know I don't.  Help me out here Matt.